The present invention relates to a cooling system for an engine.
Conventionally, known cooling systems for vehicles form a plurality of coolant flow paths passing through an engine body (cylinder head or cylinder block) or auxiliary machinery (heater core, exhaust gas recirculation (EGR) device, etc.), and are provided with a flow rate control valve for controlling coolant flow rates of the respective coolant flow paths (e.g., JP2013-224643A). Such a cooling system restricts the flow of the coolant into the engine body by the flow rate control valve while the engine is being warmed up after a cold start so as to stimulate a temperature increase of the engine body. When the temperature of the engine body becomes high, the cooling system cancels the flow restriction of the coolant into the engine body so as to cool the engine body. A water pump is disposed upstream of the flow rate control valve and discharges the coolant.
During such a flow restriction, the coolant paths on the upstream side of the flow rate control valve are under a high hydraulic pressure caused by a discharging pressure of the water pump. If the flow restriction is canceled under the high hydraulic pressure, a large amount of coolant temporarily flows into the engine body and causes a temperature decrease of the engine body.
Therefore, with the cooling system of JP2013-224643A, a coolant flow path which passes through the auxiliary machinery but does not pass through the engine body (hereinafter, referred to as “the engine-bypass flow path”) is provided, and the coolant is flowed into the engine-bypass flow path prior to canceling the flow restriction in the flow path passing through the engine body (hereinafter, referred to as “the through-engine flow path”). Thus, overcooling of the engine body by the introduction of the large amount of coolant due to the high hydraulic pressure on the upstream side of the flow rate control valve is suppressed.
Meanwhile, in JP2013-224643A, when the coolant is not flowing into the engine-bypass flow path (when the coolant dwells in the engine-bypass flow path without flowing), the temperature of the coolant within the engine-bypass flow path is low. Therefore, immediately after the flow rate control valve switches the flow path by the flow rate control valve to change the state where the coolant is not flowing into the engine-bypass flow path into a state where the coolant is flowing thereinto, the low-temperature coolant currently dwelling in the engine-bypass flow path without flowing flows into the engine body, and therefore, the temperature of the engine body temporarily decreases, and ignitability of the engine may degrade.